26 THE STRUGGLE FOR EXISTENCE 



investigated from a certain general viewpoint as (1) intensity of 

 competition, (2) competition in mixed populations, (3) the influence 

 of environment upon competition in mixed cultures, and (4) the role 

 of the quantitative relations between species at the beginning of their 

 struggle. Among animals the processes of the struggle for existence 

 are much more complex, and as yet one cannot speak of any general 

 principles. In this connection an investigation of the elementary 

 processes of the struggle for life in strictly controlled laboratory con- 

 ditions is here particularly desirable, and the material just presented 

 will be of great help to us in the choice and arrangement of the corre- 

 sponding experiments. 



